1. Field of the Invention
The present invention relates to an improvement of a solid state imaging device of a wafer-level chip size package type.
2. Description Related to the Prior Art
A digital camera and a digital video camera with use of a solid state imaging device such as a CCD, a CMOS, and the like is in widespread use. A conventional solid state imaging device has a structure where an image sensor chip which is a semiconductor substrate is contained in a package and is sealed by a transparent glass rid. Because of increasing demand for a mobile phone or the like with the image-taking function, the solid state imaging device is required to be smaller.
As a packaging method to make the solid state imaging device smaller, a wafer-level chip size packaging (hereinafter WLCSP) is disclosed in U.S. Pat. No. 6,483,179. In the WLCSP, a semiconductor device package is obtained by dicing the wafer after packaging is completed in a semiconductor wafer process. A solid state imaging device manufactured by the WLCSP can largely reduce its size in comparison with the conventional solid state imaging device manufactured by the ceramic packaging.
It is known that unnecessary radiation noise (EMI) emitted from the solid state imaging device adversely affect adjacent electronic devices. For example, in the CCD, the unnecessary radiation noise is caused by a horizontal transfer pulse and a reset signal both running at high clock rate, and a CCD-RAW signal synchronizing with the horizontal transfer pulse. To prevent the generation of the unnecessary radiation noise, the solid state imaging devices are covered with shields, in Japanese Patent Laid-Open Publications No.05-329100 and No.05-056916.
In addition, conventionally, a zener diode is connected to a CCD output terminal of the solid state imaging device such that capacitance components of the zener diode smoothes the output waveform, to prevent the generation of the unnecessary radiation noise.
However, because the solid state imaging device of the WLCSP type is very small, it is difficult to cover the solid state imaging device without blocking the use area of the image sensor. Further, the merit of being small is spoiled if the solid state imaging device of the WLCSP type is covered with the shield. In addition, the zener diode is required to position as near to the solid state imaging device as possible, because the effect of preventing the unnecessary radiation noise becomes better when the zener diode connects to the solid state imaging device at the position closer to the solid state imaging device.